1. Field of the invention
The present invention relates to a data transmission system for transmitting data in packets and used in the field of, for example, office automation system, factory automation system, home automation system, or the like.
2. Description of the Prior Art
The data transmission system which the present invention is involved is used, for example, in a remote control system for controlling various equipment and appliances, such as, lights, and air conditioners. The system includes, e.g., a number of stations in which one station may be designated as a center. The stations are connected to each other by a common bus line. The data transmission may be carried out from one station to another station, or from one station to a plurality of stations, simultaneously. To carry out the system with the least error operations as possible, it is very important to acknowledge, at the sending station, that the information data is correctly sent to the required station(s). To this end, the receiving station sends back an answer-back through the same bus line to the sending station where the information data was sent.
The sending of the information data along the bus line to a destination station is done such that the information data is combined with other data, such as address data, error check data, etc. The combined data is generally referred to as a packet. Also, when sending the data along the bus line, a predetermined time interval is necessary between packets so as to prevent any interference between the data, as discussed in Japanese Utility Model application No. 58-196415 or in Japanese Patent Publication (examined) No. 58-45059.
According to the prior art system, the answer-back contains the same information data as that was sent to the receiving station. Thus, at the sending station, an information data storage is provided for temporarily storing the information data to be sent, and also a comparator is provided for comparing the stored data with the information data contained in the answer-back. Therefore, each station must have the information data storage and the comparator, which will result in a bulky station and a high manufacturing cost.